Daniel Duplaisir, left, is accused of blackmailing Texas A&M University professor James Aune. (KTRK-TV/ABC News)(HOUSTON) -- Before professor James Aune leapt to his death from a Texas A&M parking garage, he sent a final text message to the man authorities allege lured him into an underage online sex extortion plot.

"Killing myself now And u will be prosecuted for blackmail," Aune wrote. He pressed the send button one minute before he jumped to his death on Jan. 8, according to a federal complaint.

The man who authorities said received that text message, Daniel Duplaisir, 37, pleaded not guilty in a Houston federal court Tuesday to a felony charge of sending threatening communications.

Authorities said Aune, 59, was chairman of the Department of Communications at Texas A&M University and he became trapped in an elaborate extortion plot orchestrated by Duplaisir that threatened to turn his world upside-down.

The scheme involved using explicit photos Duplaisir allegedly took of an underage female relative to lure men into an online relationship and share their names and phone numbers, according to the federal complaint. The suspect would then contact the victim posing as an angry father demanding money to pay for the daughter's therapy, court documents state. The scam has been operated by Duplaisir since at least 2011, the charges claim.

Aune, a married father of two sons, took the bait, believing he was conversing with a girl named Karen McCall, according to communications detailed in the complaint.

In December, the professor received his first communication from Duplaisir, who authorities said posed as the girl's angry father who had discovered the affair.

According to the complaint, Duplaisir demanded $5,000 to pay for his daughter's counseling and a computer he said he had broken to keep her off the Internet. If Aune didn't pay, he said, he would contact Texas A&M University and authorities.

"I answered and said I would do whatever he wanted….I sent him $1,000 and then promised more in January," Aune wrote in an email sent to the address for Karen McCall, according to the complaint.

"I am s***-scared about this, and can't figure out how to come up with more money," he said, telling Karen he couldn't talk to her anymore.

Beginning at 9:04 a.m. Jan. 7, Duplaisir sent a series of text messages and emails to the professor demanding more money and giving him a deadline of Jan. 8 at 12 p.m., according to the complaint.

"If I do not hear from you I swear to God Almighty that the police, your place of employment, students, ALL OVER THE INTERNET…ALL OF THEM will be able to see your conversations, texts, pictures you sent," Duplaisir wrote, according to the complaint.

"And if by some miracle you get away with this I will use every chance I get to make sure every place or person associated with you knows and see what you have done," he said. "Last chance, you better make right move."

At 10:30 a.m. the next day, Aune killed himself.

Aune's widow, Miriam, told authorities that in mid-December her husband told her he had become "involved in sexually explicit chat" with a minor he had met online and that he was now being extorted by her father. She told authorities that her husband had paid $1,500 to someone using Green Dot banking's reloadable debit cards.

A subpoena of Green Dot bank records revealed the money had gone to Daniel Duplaisir of Metairie, La. Furthermore, surveillance video at a Lowe's showed Duplaisir making a $114.04 purchase with one of the cards, according to the complaint.

Duplaisir was arrested in January.

The suicide of the popular professor stunned the Texas A&M community.

"Jim always made the time to chat, email, share a smoke or a story with his many friends, students, and colleagues," his obituary on the school's website said. "We will all miss his witty banter, his kind words of encouragement, and his gentle nudges to believe in ourselves.

Texas A&M officials did not immediately respond to an interview request.